Tetramethyl-1,2-dioxetane chemiluminescence

Tetramethylammonium ozonide, 736 Tetramethyl-l,2-dioxetane (TMD) chemical titration, 1224 chemiluminescence, 1221, 1234 quantum yield standard, 1224, 1226 N,N, N, A -Tetramethyl-p-phenylenediamine hydrogen peroxide determination, 735, 631, 633... 

Emission of phosphorescence by 1,2-dioxetanes and a-peroxylactones has also been observed, but is quite rare. Thus, in degassed acetonitrile the 430 nm emission exhibited by the tetramethyl-l,2-dioxetane (7) has been assigned to acetone phosphorescence. Similarly, this acetone phosphorescence has been detected for the dimethyl-a-peroxylactone. ° For the acetyl derivative (19), both the n,TT fluorescence and phosphorescence of 2,3-butanedione have been reported. Thus, if the photoexcited luminescence spectrum of the carbonyl product is known or can be readily measured, the chemiluminescence spectrum can be used as corroborative structure confirmation of the 1,2-dioxetane or a-peroxylactone. 

Oxidation of luminol (see Example 7.22) and thermolysis of endoperox-ides or 1,2-dioxetanes provide important examples of chemiluminescent reactions. Tetramethyl-1,2-dioxetane (181) has been studied in great detail the thermolysis is clearly first order and the activation enthalpy in butyl phthal-ate is A// 27 kcal/mol. The enthalpy difference between the reactants and ground-state products is A// = -63 kcal/mol. 

Figure 7.57. State correlation diagram for the chemiluminescence reaction of tetramethyl-1,2-dioxetane (by permission from Turro, 1978).

Dioxetanes such as tetramethyl-1,2-dioxetane (525) are known to undergo thermal decomposition to form two carbonyl compounds via a concerted or stepwise (radical) mechanism, accompanied by chemiluminescence (Section 5.6) (Scheme 6.254).135,511,1440 The degradation of 525 results principally in acetone phosphorescence (2max = 430 nm) and the reaction is very sensitive to quenching by oxygen. 

The chemiluminescent autoxidation of tetrakis(dimethylamino)-ethylene (35) is spectacular.62 Ground-state oxygen is sufficiently reactive to produce the dioxetane laq, presumably via electron transfer, radical cage coupling, and cyclization [Eq. (22)]. Besides tetramethyl-... 

The typical reaction of 1,2-dioxetanes is thermal decomposition. On warming tetramethyl-1,2-dioxetane in benzene or other solvents, blue light is emitted. Such a phenomenon is known as chemiluminescence [11]. It has been demonstrated that, according to the principle of conservation of orbital symmetry, one mole of acetone in an electronically excited state is formed. In this way, an electronically excited molecule (symbolized by ) is created by a thermal process. With emission of light, the ground state is restored ... 

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